Abstract
Asymmetric transmission (AT) devices are fundamental elements for optical computing and information processing. We here propose an AT device consisting of a pair of coupled complementary subwavelength gratings. Different from previous works, asymmetric dielectric environment is employed for unidirectional excitation of surface plasmon polaritons (SPPs) and thus asymmetric optical transmission, and near-field coupling effect inherent in the coupled complementary structure is exploited to enhance forward transmission and AT behavior, and determine operation bandwidth as well. The influence of asymmetric dielectric environment, effect of vertical and lateral couplings, interactions of electric- and magnetic-dipole moments and the realization of Kerker conditions, are investigated in depth to unearth the AT mechanism and performance. High-performance AT with large forward transmittance of 0.96 and broad bandwidth of 174 nm is achieved at wavelength 1250 nm. Our work helps people to gain a better understanding of near-filed coupling effect in coupled complementary structures, expand their application fields, and it also offers an alternate way to high-performance AT devices.
Highlights
Asymmetric transmission (AT) devices are fundamental elements for optical computing and information processing
We propose and demonstrate a strong direction-selective asymmetric transmission (AT) device based on coupled complementary gratings
It consists of an upper metallic grating, a lower metallic grating which is the Babinet complementary structure of the upper one, and a dielectric spacer layer between them
Summary
Asymmetric transmission (AT) devices are fundamental elements for optical computing and information processing. Different from previous works, asymmetric dielectric environment is employed for unidirectional excitation of surface plasmon polaritons (SPPs) and asymmetric optical transmission, and near-field coupling effect inherent in the coupled complementary structure is exploited to enhance forward transmission and AT behavior, and determine operation bandwidth as well. AT effects based on unidirectional excitation of SPPs have been studied by utilizing double gratings with different periods[20,21,22], multilayer metasurfaces[23], and asymmetric metallic gratings with one or multiple subwavelength slits[24,25]. Substrate utilized to unidirectionally excite SPPs, and near-field coupling inherently existing between the upper and lower gratings enables electric- and magnetic-dipole moments to interact with each other, significantly enhancing forward transmittance, asymmetric transmission and operation bandwidth
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